This invention relates to a boron-coating ionization chamber for detecting and measuring the level of neutron flux existing within a nuclear reactor.
Chmabers of this type are also known and the general principle on which tehy are based is described for example in French Pat. No. 2,133,798. Boron chambers filled with an ionizable gas are usually constructed with two electrodes which are brought to different potentials and at least one of which is coated with boron. The neutrons generated in the nuclear reactor use the (n,.alpha.) reaction to produce lithium nuclei and .alpha.-particles which cause ionization of the filling-gas atoms. The ions thus created are transported towards the two electrodes and collected on these latter. The measurement of the corresponding charges or in other words the measurement of the current which circulates between the two electrodes provides a measurement of the neutron flux to which the ionization chamber is subjected.
Ionization chambers (having a coating of boron or of fissile material) are subjected to high values of neutron flux and to considerable vibrations in nuclear reactors of the pressurized-water type and boiling-water type; under such critical and exacting conditions of operation, ionization chambers of known types have exhibited a degree of reliability which is too low to ensure a sufficiently long service life and have also proved excessively sensitive to vibrations.
In order to carry out measurements which are adapted to the intended use of the reactor, it also proves necessary to divide the ionization chamber into a plurality of electrically independent modules, the connection of such modules being left to the choice of the operator for a predetermined application.
Special care has to be given to the mechanical structure of the chamber in order to compensate for any expansion and to prevent any fatigue of materials which would result in damage, defective leak-tightness and faulty insulation of the electrical bushings.